A conventional `omni` broadband personal communication system (PCS)/cellular base station, which employs a wideband digital transceiver and associated omnidirectional antennas, cannot provide high capacity in a multiple base station environment. Due to the presence of co-channel interferers, the base station either has no neighbors or has a high channel reuse factor (e.g., K=11 or greater). Unfortunately, a high reuse factor means that only a small fraction (e.g., on the order of one-tenth) of the available power of the receiver is being used.
As a consequence, an omni base station suffers a significant cost disadvantage compared with those that employ narrowband systems operating at only a limited number of channels, since receiver cost is the same regardless of whether it is being fully utilized. For example, for a 5 MHz PCS GSM system, twenty-four RF channels having eight voice channels per RF channel provides 192 total channels. At a frequency reuse factor of K=11, two RF channels at eight voice channels/RF channel provides sixteen available channels, resulting in an Erlangs/base station at a grade of service of 0.02 equal to 9.83.
One way to increase capacity is to implement a sectorized wideband base station employing directional antennas to subdivide the spatial coverage (e.g., into three 120 sectors). Although reducing the number of potential interferers, this approach suffers from reduced channel use (e.g., K=4, which allows use of only one-fourth of the available channels). In addition, a sectorized wideband radio suffers trunking efficiency loss. For example, for the above 5 MHz PCS GSM example, at K=4, six RF channels at eight voice channels per RF channel yields 48 total channels, or 16 channels per sector for three 120.degree. spatial sectors. At an Erlangs/sector of 9.83, the resulting Erlangs/base station is somewhat improved over that of a conventional omni base station at (9.83.times.3)=29.49 Erlangs.